1. The Field of the Invention
The present invention relates to vehicle tire air pressure maintenance systems. More specifically, the invention relates to dual-function tire inlet valves.
2. Technical Background
Monitoring and maintaining proper tire air pressure for vehicles has long been an important maintenance item carried out by a vehicle owner. In the past, vehicle owners regularly checked tire pressure because low-pressure tires were easily noticed. However, as tire technology has advanced, low tire pressure has become more difficult to notice by simple observation. This, and a perception that more advanced tires experience fewer slow leaks, has lead vehicle owners to stop or drastically reduce monitoring the tire pressure for their vehicles.
Tires are still subject to leaks. Generally, the leaks are slow and may not always completely deflate the tire. The leaks may be attributable to permeability of the tire material by failed tire valves, an opening between the tire and rim, or a puncture of the tire or inner tube by a foreign object such as glass or a nail. Natural leaks may reduce the pressure by as much as one pound per square inch (psi) per month. Seasonal temperature changes also reduce tire pressure by one psi for every drop of 10 F. degrees in temperature. Changes in altitude also affect tire pressure.
Low tire pressure may cause significant problems. Studies relied upon by the National Highway Traffic Safety Administration (NHTSA) indicate that low-pressure tires reduce vehicle safety. For example, lower pressure causes more wear on the tire sidewalls, which may lead to premature failure. The NHTSA estimates that 23,464 crashes were a result of under-inflated tires.
Low tire pressure also reduces the life of the tire. Data from Goodyear and Michelin indicate that 20% under-inflation can reduce tire life by up to 50%. Low tire pressure causes the tire tread to wear non-uniformly, which may also cause premature failure of the tire. Tire costs, particularly for the trucking industry, are the second highest operating expense behind fuel.
Low tire pressure reduces the fuel economy of the vehicle. Tires with lower pressure require more energy to rotate. Goodyear indicates that tires that are 15% under-inflated result in a 2.5% increase in fuel consumption.
Finally, a federal government agency is proposing to require tire pressure monitoring systems on all new cars, trucks, and multipurpose passenger vehicles. (See xe2x80x9cTire pressure monitoring systems; controls and displaysxe2x80x9d NHTSA, 49 CFR Part 571) This proposal would require tire pressure systems to notify the driver if the tire pressure descends below a threshold level. Such a proposal may be very costly if conventional tire pressure maintenance and monitoring systems must be used and maintained (e.g., by replacing batteries, etc.).
In response to the problems caused by low tire pressure, efforts have been made to provide devices and systems that monitor and/or maintain the pressure in a vehicle""s tires. Known pressure maintenance efforts have generally focused on mechanisms for adding small amounts of air to the tire while the tire rotates to compensate for losses due to leaks.
These pressure maintenance devices include external or internal compressors that compress ambient air into an interior chamber of the tire. For the tire pressure maintenance systems to operate, air must pass into the tire via an inlet valve either before or after compression. Additionally, tires with pressure maintenance devices must have an inlet valve that allows users to manually adjust the tire pressure and allows tire professionals to service the tires.
Therefore, tires equipped with pressure maintenance devices utilize two inlet valves, one for pressure maintenance and another for traditional tire valve functions. Conventional tire inlet valves include a valve body, a valve spring, and a valve stem. The stem typically includes a valve actuator and a valve seal. The valve spring biases the valve seal against the valve body to close the valve. A user can open these conventional valves by engaging the actuator to compress the spring and move the valve seal away from the valve body.
The introduction of additional tire inlet valves for use with pressure maintenance systems is problematic during repair of damaged tires. Tire valves typically extend through the rim of the wheel. The valve must be withdrawn from the rim to service the tire and then reinserted through the rim to assemble the wheel. A second tire inlet valve presents many challenges to tire professionals that must service tires with tire pressure maintenance systems. For example, the position of the valve relative to the rim is important to ensure that the valve functions properly. A second tire valve will increase the incidence of errors in tire maintenance and the possibility of valve failure. Additionally, the costs of tire maintenance will increase with the increased complexity of the repair procedures.
Furthermore, tires often loose air pressure through valve failure. The introduction of a second tire inlet valve increases the probability of air pressure loss due to valve failure.
Accordingly, it would be an advancement in the art to provide a fail-safe tire inlet valve that can be used with existing tire pressure maintenance and monitoring systems. It would be a further advancement to provide a tire pressure maintenance and monitoring system that allows automatic and manual adjustment without requiring multiple valve structures to extend from the tire body. Additionally, it would be an advancement in the art to provide a tire inlet valve that selectively allows ambient air into a tire pressure maintenance and monitoring system only under certain conditions.
The apparatus and method of the present invention have been developed in response to the present state of the art, and in particular, in response to the problems and needs in the art that have not yet been fully solved by currently available tire pressure maintenance and monitoring devices. Thus, the present invention provides a tire pressure maintenance system with a dual-function tire inlet valve that is simple, inexpensive, and safe.
In one embodiment, the dual-function tire inlet valve is mountable on a tire in communication with a compressor in a tire pressure maintenance system. The inlet valve has a conduit with an exterior end and an interior end. When the inlet valve is mounted on a tire, the exterior end of the conduit is in fluid communication with an ambient air supply and the interior end is in fluid communication with an interior chamber of the tire. The dual-function inlet valve also includes a first check valve positioned adjacent to one end of the conduit and a second check valve adjacent to the other end of the conduit. The first check valve is automatically opened only when the compressor is active and the tire is rotating about its axis with at least a pre-determined velocity. The second check valve opens only upon manual actuation.
A pump channel may be formed within the conduit and in fluid communication with the compressor between the first and second check valves. The first check valve may preferably be positioned adjacent to the exterior end of the conduit with the second check valve positioned adjacent to the interior end of the conduit.
The conduit may comprise a sleeve that is removably disposed in a shell surrounded by an encasement configured for mounting on a conventional tire. A portion of the sleeve may have a threaded outer surface and a corresponding portion of the shell may have a threaded inner surface such that the threaded outer surface of the sleeve mates with the threaded inner surface of the shell when the sleeve is disposed in the shell.
The sleeve, the shell and the encasement of the dual-function tire inlet valve of the present invention may be configured to associate with conventional external tire valve devices such as pumps and pressure gauges. The tire inlet valve may further comprise an air-filter cap to allow ambient air into the valve while preventing the entrance of foreign objects.
The encasement, the shell, and the sleeve may be provided with pump passages to allow fluid communication between the pump channel and the compressor. The tire inlet valve may further comprise a sleeve seal between the sleeve and the shell between the ambient air supply and the pump passages. The sleeve seal ensures that ambient air only enters the pump channel via the first check valve. A bottom seal may also be provided between the sleeve and the shell between the pump channel and the interior chamber of the tire. The bottom seal ensures that air leaving the interior chamber of the tire through the tire inlet valve exits via the second check valve.
The first check valve of the present invention may be a modified Schrader-type tire valve and the second check valve may be a standard Schrader-type tire valve. Alternatively, the first check valve may comprise a first valve body, a first valve stem extending through the first valve body, and a first valve spring associated with the first valve stem. In this embodiment, the first valve stem includes a first valve actuator and a first valve seal. The first valve spring biases the first valve stem such that the first valve seal is biased toward the first valve body in a closed position. In this embodiment, the second check valve may be similarly designed with a second valve body, a second valve stem including a second valve actuator and a second valve seal, and a second valve spring.
In this configuration, engagement of the first valve stem opens the first check valve, and engagement of the second valve stem opens the second check valve. It should be noted however, that the first valve stem may be engaged without engaging the second valve stem. Preferably, automatic inertial engagement of the first valve stem does not engage the second valve stem.
In one embodiment of the dual-function tire inlet valve of the present invention, the spring constant of the first valve spring and the mass of the first valve stem are chosen such that the first check valve opens automatically only when the compressor is active and the tire is rotating about its axis with at least a pre-determined velocity. Additionally, the spring constant of the second valve spring and the mass of the second valve stem are chosen such that the second check valve is only manually opened. The first valve spring may have a spring constant ranging from about 0.00280 lbf/in to about 0.00290 lbf/in, and the first valve stem may have a mass ranging from about 0.00015 pounds to about 0.00017 pounds. More preferably, the first valve spring may have a spring constant of about 0.002855 lbf/in, and the first valve stem may have a mass of about 0.000161 pounds.
In the dual-function tire inlet valve of the present invention, the first check valve will only open automatically if the compressor is active and if the fire is rotating about its axis with at least a pre-determined velocity. In a preferred embodiment the pre-determined velocity of the tire rotation corresponds to a velocity ranging from about 10 miles per hour to about 50 miles per hour. More preferably, the pre-determined velocity of the tire rotation corresponds to a velocity of about 40 miles per hour.
According to one alternative embodiment, an inlet valve may be configured for use with a compressor that draws ambient air and injects it into the tire through the inlet valve. The inlet valve may then have a first check valve disposed in its interior and configured to open when the compressor is active and the tire is rotating with the desired angular velocity. The first check valve allows the compressor to add air to the tire. A second check valve is disposed at an exterior end to prevent direct communication between the interior chamber of the tire and ambient air unless the inlet valve has been manually actuated to open the second check valve.
The present invention is also directed to a method for allowing ambient air into a tire pressure maintenance system. The method is performed by sealing a pump channel from an ambient air supply with a first check valve and sealing the pump channel from an interior chamber of a tire with a second check valve. The pump channel is in fluid communication with the tire pressure maintenance system, and the first check valve is automatically opened only when the tire pressure maintenance system is pulling air from the pump channel and the tire is rotating about its axis with at least a pre-determined velocity. The second check valve is only opened manually.
These and other features and advantages of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.